docs: def and_evaluator(conditions, leaf_evaluator):
    """ Evaluates a list of conditions as if the evaluator had been applied
    to each entry and the results AND-ed together.
  
    Args:
      conditions: List of conditions ex: [operand_1, operand_2].
      leaf_evaluator: Function which will be called to evaluate leaf condition values.
  
    Returns:
      Boolean:
        - True if all operands evaluate to True.
        - False if a single operand evaluates to False.
      None: if conditions couldn't be evaluated.
    """
    saw_null_result = False
  
    for condition in conditions:
      result = evaluate(condition, leaf_evaluator)
      if result is False:
        return False
      if result is None:
        saw_null_result = True
  
    return None if saw_null_result else True